The key here is that the maunfacturers are not forcing anyone to buy any of the new equipment they are producing. They make new balls and yes, a lot are just older balls in a different color or small change to the cover or core, etc., but we are not forced to purchase them. I would think that the majority of bowlers who buy a new ball are doing so to replace an older one that has run its course, similar to buying a newer vehicle when your current one starts to fall apart or not run as smoothly as it did when new.
As Avabob states, you really can't blame the companies, they are only trying to make money and need bowlers to buy their equipment to do so, especially since the overall number of bowlers is stagnant or even declining.